Method for controlling the amount of silicon contained as an impurity in high carbon ferrochromium

ABSTRACT

A method for controlling the amount of silicon contained as an impurity in high carbon ferrochromium which, when there is smelted high carbon ferrochromium by reducing raw chromium ores in a submerged arc furnace, consists in mixing fine chromium ores being used with proper amounts of other crushed raw materials rich in magnesium oxide or aluminum oxide fully to match the weight ratio of the magnesium oxide to the aluminum oxide both contained as impurities in said raw chromium ores, whereby the proportion of silicon contained in the alloyed product can be controlled as desired by carrying out said mixing to such extent that the weight ratio of the magnesium oxide to the aluminum oxide present in the mixture attains a value indicated by any point on the correlation curve of the attached chart.

United States Patent Eda et al.

[ METHOD FOR CONTROLLING THE AMOUNT OF SILICON CONTAINED AS AN IMPURITY IN HIGH CARBON FERROCHROMIUM [75] Inventors: Shinjiro Eda, Yokohama; Hiroshi Iwabuchi, Niigata; Kazuo Yamagishi, Yokohama; Keiiti Nakagawa, Shinminato, all of Japan [73] Assignee: Nippon Kokan Kabushiki Kaisha,

Tokyo, Japan [22] Filed: Mar. 2, 1972 [21} Appl. No.: 231,326

[30] Foreign Application Priority Data Mar. 10, l97l Japan 46/12688 [52] US. Cl. 75/12, 75/l30.5 [51] Int. Cl. C21c 5/52 [58] Field of Search 75/10-13, 130.5

[56] References Cited UNITED STATES PATENTS 2,934,422 4/1960 Udy 75/11' SILICON CONTENT IN THE HIGH CARBON FERROCHROMIUM (70) N (N J5 U1 03 \l (D (D 3,765,871 Oct.16,1973

2,674,529 4/1954 Crafts 75/12 1,923,471 8/1933 Arnold 75/12 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Peter D. Rosenberg AttorneySolon B. Kemon et al.

[ 5 7] ABSTRACT A method for controlling the amount of silicon contained as an impurity in high carbon ferrochromium which, when there is smelted high carbon ferrochromium by reducing raw chromium ores in a submerged arcfurnace, consists in mixing fine chromium ores being used with proper amounts of other crushed raw materials rich in magnesium oxide or aluminum oxide fully to match the weight ratio of the magnesium oxide to the aluminum oxide both contained as impurities in said raw chromium ores, whereby the proportion of silicon contained in the alloyed product can be controlled as desired by carrying out said mixing to such extent that the weight ratio of the magnesium oxide to the aluminum oxide present in the mixture attains a value indicated by any point on the correlation curve of the attached chart.

7 Claims, 1 Drawing Figure 0.5 0.6 0.7 d8 d9 Io III I2 I3 I4 I5 IE -17 Ie I9 20 WEIGHT RATIO OF M O To A2 0 CONTAINED IN CHARGING MATERIALS METHOD FOR CONTROLLING THE AMOUNT OF SILICON CONTAINED AS AN IMPURITY IN HIGH CARBON FERROCHROMIUM DETAILED DESCRIPTION OF THE INVENTION TABLE 1. Grades of High Carbon Ferrochromium (JIS) No. Symbol Component mark Cr C Si P S 1 FCrH 65 to 70 6.0 1.5 0.04 0.08 under under under under 2 FCrH, 60 to 65 2.0 2.0 0.04 0.08 under under under under 3 FCrH, 60 to 65 2.0 2.0 0.04 0.06 under under under under 5 FCri-i 55 to 60 8.0 8.0 0.04 0.05 under under under under In fact, however, steel makers using'high carbon ferrochromium often demand other grades of said alloy outside of the 11S specification shown in Table 1 above, as is particularly the case with the content of silicon. For example, some steel makers sometimes ask for high carbon ferrochromium containing 6.5% max. of carbon and from 2 to 3% of silicon or the one containing 6.0% max. of carbon and 1% max. of silicon. To meet such special request, makers of said ferroalloy are considerably perplexed with the selection of the description of raw chromium ores and additionally by the determination of the particle size of crushed chromium ores, slag composition, coke ratio and operating voltage. While the carbon content of the alloyed product is relatively easy to control by adjusting the coke ratio and operating voltage, the silicon content is difficult to control by any combination of the abovementioned factors, particularly when it is practically impossible for the ferroalloy makers to use raw chromium ores having a different description from that which they customarily specify.

The object of this invention is to provide a method for easily manufacturing high carbon ferrochromium containing desired amounts of metallic impurity silicon from raw chromium ores of any description.

This object can be attained in accordance with the present invention by mixing raw chromium ores being used with proper amounts of other raw materials rich in magnesium oxide or aluminum oxide according to the correlation curve (indicated in the figure of appended drawing) found by the present inventors for the first time to exist between the weight ratio of the magnesium oxide to the aluminum oxide both contained in the mixed ores so as to bring said ratio to a sufficient level to obtain a desired silicon content in the ferrochromium product, and finally smelting the raw materials thus mixed.

The single curve shown in the chart of appended figure was obtained from a large number of experiments carried out by the present inventors for the first time, as represented by the numerous plotted points on the chart. Said curve presents a correlation between the 0.6 to 2.0 weight ratio of the magnesium oxide to the aluminum oxide both contained in the raw materials and the 9 to 0.5 silicon content of high carbon ferrochromium obtained from the materials.

Speaking conversely, application of the aforesaid correlation curve enables high carbon ferrochromium to be manufactured from a particular raw chromium ore with the silicon content controlled to be within the range of 0.5 to 9%. The process of said manufacture only consists in homogeneously mixing fine raw chromium ores being used with proper amounts of other raw materials rich in magnesium oxide or aluminum oxide, and controlling the weight ratio of the magnesium oxide to the aluminum oxide both contained in the mixed raw materials so as to cause the silicon content of a ferrochromium product to have a prescribed value falling within the range of from 0.5 to 9%.

Raw materials rich in magnesium oxide include, for example, magnesia clinker, dolomite, magnesite, dunite and serpentine, and raw materials rich in aluminum oxide include, for example, corundum, bauxite, hydrated aluminous ore and aluminous shale.

It is already known to those skilled in the art that, when the aforementioned mixed raw materials are smelted in a submerged arc furnace, they should preferably be pelletized or briquetted in advance.

As previously mentioned, this invention enables the amount of silicon contained as an impurity in the ferroalloy product to be easily controlled to any desired value falling within the aforesaid range regardless of the composition of raw chromium ores being used.

The principle of this invention may be applicable not only to the manufacture of high carbon ferrochromium but also, as naturally expected, to the production of high carbon ferromanganese, high carbon ferromolybdenum, high carbon ferrotitanium and high carbon ferronickel. The manufacture of the latter group of ferroalloys may be effected simply by experimentally determining a correlation curve similar to that illustrated in the appended drawing. I

There will now be described the examples in which there were used raw materials having a composition given in Table 2 below.

Weight Composition (percent) ratio of MgO/ Raw material C1203 F00 MgO A1203 SiOz A1203 Fine chromium ore... 54. 22 14.18 10. 43 11.30 4.02 0.92 Lump chromium ore A 43.43 12.43 16.16 11.34 7. 73 1.41 Lump chromium Bauxite above with weight per cent of fine powders of the magnesia clinker of said Table, followed by pelletization, then the weight ratio of the magnesium oxide to the aluminum oxide contained in the mixture indicated about 1.7. The pelletized mixture was smelted by the customary process in a 3,000 KVA electric submerged arc furnace, easily obtaining high carbon ferrochromium containing a desired amount of silicon. Power consumption was 3,730 KWH per 1,000 Kg of product. This power requirement was substantially little different from 3,800 KWH used when the raw material only consisted of the lump chromium ore A of Table 2. Example 2 This example relates to the manufacture of high carbon ferrochrornium'containing.2 to 3% of silicon as an impurity. In this case, the conventional method failed to produce high carbon ferrochromium having said desired silicon content from the fine chromium ore of Table 2, though it effected said production from the lump chromium ore A of said Table.

When there were mixed according to the method of this invention thesame fine chromium ore of Table 2 I 4 then the weight ratio of the magnesium oxide to the aluminum oxide contained in the mixture amounted to about 1.4. The pelletized mixture was smelted in the same manner as in Example 1, easily obtaining high carbon ferrochromium containing the desired amount of silicon. Power consumption was about 3,800 KWl-l per 1,000 Kg of product.

Example 3 There was prepared referential high carbon ferrochromium according to the conventional method only from the screened powders of the lump chromium ore B of Table 2. As apparent from the appended curve chart, however, this process failed to provide high carbon ferrochromium containing 2 to 3% of silicon as an impurity.

When said screened powders of the lump chromium ore B were mixed according to the method of this invention with 7 weight per cent of the bauxite of Table 2, followed by pelletization, then the weight ratio of the magnesium oxide to the alluminum oxide contained in the mixture indicated about L4. The pelletized mixture was smelted in the same manner'as in Example 1, easily obtaining high carbon'ferrochromium containing 2.3% of siliconas an impurity. in this case, power consumption was as low as about 3,000 KWH per 1,000 Kg of product. i

What we claim is:

l. A method for controlling the amount of silicon contained as an impurity in a high carbon ferrochromium containing between about 2 to 8% by weight carbon which comprises selecting a silicon content for said ferrochromium between about 0.5 to 9% by weight, providing a material mixture by mixing raw chromium ore with an amount of other raw material rich in oxide selected from the group consisting of aluminum oxide and magnesium oxide so that the quantities of magnesium oxide and aluminum oxide in said material mixture substantially correspond to the point on the curve of the annexed drawing at which said selected silicon content and the weight ratio of MgO and A1 0 intersect and smelting said material mixture charged in a submerged arc furnace in the presence of a reducing.

agent.

. 2. The method of claim 1 wherein said other raw material is selected from the group consisting of magnesia clinker, dolomite, magnesite, dunite, serpentine, corundum, bauxite, hydrated aluminous ore and aluminous shale.

3. The method of claim 1 wherein said material mixture is pelletized or briquetted before charging in said are furnace.

4. The method of claim 1 wherein said reducing agent is coke.

5. A method for producing ferrochromium containing between about 2 to 8% by weight carbon and a controlled amount of silicon between about 0.5 to 9% by weight which comprises:

selecting a silicon content for said ferrochromium between about 0.5 to 9% by weight,

providing a material mixture by mixing raw chromium ore with other raw material rich in oxide selected from the group consisting of aluminum oxide and magnesium oxide so that the quantities of magnesium oxide and aluminum oxide in said material mixture substantially correspond to the point on the curve of the annexed drawing at which said selected silicon content and the weight ratio of MgO and M 0 intersect, forming said material mixture into shaped bodies selected from the group consisting of pellets and briquettes, and smelting said shaped bodies of material mixture in the presence of coke in a submerged arc furnace.

6. The method of claim 5 wherein said outer raw material is rich in magnesium oxide selected from the group consisting of magnesia clinker, dolomite, magnesite, dunite and-serpentine. I

7. The method of claim 5 wherein said other raw material is rich in aluminum oxide selected from the group consisting of corundum, bauxite, hydrated aluminous ore and aluminous shale. 

2. The method of claim 1 wherein said other raw material is selected from the group consisting of magnesia clinker, dolomite, magnesite, dunite, serpentine, corundum, bauxite, hydrated aluminous ore and aluminous shale.
 3. The method of claim 1 wherein said material mixture is pelletized or briquetted before charging in said arc furnace.
 4. The method of claim 1 wherein said reducing agent is coke.
 5. A method for producing ferrochromium containing between about 2 to 8% by weight carbon and a controlled amount of silicon between about 0.5 to 9% by weight which comprises: selecting a silicon content for said ferrochromium between about 0.5 to 9% by weight, providing a material mixture by mixIng raw chromium ore with other raw material rich in oxide selected from the group consisting of aluminum oxide and magnesium oxide so that the quantities of magnesium oxide and aluminum oxide in said material mixture substantially correspond to the point on the curve of the annexed drawing at which said selected silicon content and the weight ratio of MgO and Al2O3 intersect, forming said material mixture into shaped bodies selected from the group consisting of pellets and briquettes, and smelting said shaped bodies of material mixture in the presence of coke in a submerged arc furnace.
 6. The method of claim 5 wherein said outer raw material is rich in magnesium oxide selected from the group consisting of magnesia clinker, dolomite, magnesite, dunite and serpentine.
 7. The method of claim 5 wherein said other raw material is rich in aluminum oxide selected from the group consisting of corundum, bauxite, hydrated aluminous ore and aluminous shale. 